This invention relates to hydrostatic apparatus for supporting a mobile part which moves relatively to a foundation and which comprises a bearing shoe having a bearing face containing a pressure pocket, a hydraulic servomotor which urges the shoe in the direction of the mobile part, and supply means for delivering hydraulic fluid under pressure to the pocket and the servomotor.
One apparatus of the type just mentioned is disclosed in U.S. Pat. No. 3,802,044, issued Apr. 9, 1974. In that proposal, the bearing shoe follows all displacements of the supported part, and the supporting force it furnishes is constant. Thus, in that apparatus, the position of the part being supported determines the position of the bearing shoe. This floating characteristic renders the apparatus unsuitable for applications in which the supported part must be held at a predetermined position relative to the foundation.
Another apparatus of the type under discussion is disclosed in U.S. application Ser. No. 588,582, filed June 19, 1975 (now U.S. Pat. No. 3,994,367, issued Nov. 30, 1976). This apparatus includes a spring which reacts between the shoe and the foundation, so it furnishes a supporting force which increases and decreases, respectively, as the mobile part moves toward and away from the foundation. However, it is not capable of maintaining the mobile part in a precise position relative to the foundation in situations where forces, other than weight, act in the supporting direction.